Obese trauma patients who sustain orthopaedic fractures experience increased length of stay, ICU admissions and mortality

The rising trend of obesity in the United States has been a growing concern within the healthcare system for decades. Since the early 1960s, the prevalence of obesity has more than doubled among U.S. adults, and one out of every three Americans is now considered obese according to the National Health and Nutrition Examination Survey [1,2]. Signifi cant medical comorbidities have been associated with obesity and increased Body Mass Index (BMI); these include hypertension, dyslipidemia, coronary artery disease, stroke, sleep apnea, type II diabetes mellitus and certain types of cancer. Trauma patients with higher BMIs are more likely to have increased complication rates, develop multiple system organ failure, acute respiratory distress syndrome and infections [35]. Additionally, obesity is an independent risk factor for increased morbidity and mortality following high-impact blunt force trauma and has been associated with signifi cantly longer Intensive Care Unit (ICU) lengths of stay with greater anticipated hospital costs [6,7].


Background
The rising trend of obesity in the United States has been a growing concern within the healthcare system for decades. Since the early 1960s, the prevalence of obesity has more than doubled among U.S. adults, and one out of every three Americans is now considered obese according to the National Health and Nutrition Examination Survey [1,2]. Signifi cant medical comorbidities have been associated with obesity and increased Body Mass Index (BMI); these include hypertension, dyslipidemia, coronary artery disease, stroke, sleep apnea, type II diabetes mellitus and certain types of cancer. Trauma patients with higher BMIs are more likely to have increased complication rates, develop multiple system organ failure, acute respiratory distress syndrome and infections [3][4][5]. Additionally, obesity is an independent risk factor for increased morbidity and mortality following high-impact blunt force trauma and has been associated with signifi cantly longer Intensive Care Unit (ICU) lengths of stay with greater anticipated hospital costs [6,7].
There is a well-established association between increasing BMI and the probability of sustaining a musculoskeletal injury, including certain types of fractures [8]. Furthermore, several retrospective studies have identifi ed an increased risk of postoperative complications for fractures involving the ankle, tibia, femur, humerus and pelvis [7,[9][10][11][12][13][14][15]. However, the literature regarding the clinical outcomes of hospitalized obese trauma patients who sustain fractures is limited despite the increasing prevalence of obesity among this population.
The purpose of this study was to investigate whether obesity (BMI ≥ 30kg/m 2 ) is an independent risk factor for worse outcomes in orthopaedic trauma patients who sustained a fracture or multiple fractures, utilizing a large institutional database at a level I trauma center. We hypothesized that obese patients who sustained fractures would have worse outcomes including longer hospital and ICU lengths of stay, more frequent admissions to the ICU, and increased mortality rates compared to their nonobese counterparts. Furthermore, we sought to investigate the infl uence of fracture site and the impact of fracture fi xation on the aforementioned outcomes.

Methods
This was a retrospective evaluation using data from an institutional trauma registry at an academic level I trauma center that is part of the American College of Surgeons National Trauma patients were identifi ed as all patients who sustained a traumatic injury and were diagnosed with an injury in the ICD-9-CM range of 800.0-959.9. Further inclusion criteria for trauma patients included admission to the hospital or an observation unit, transportation via emergency medical service and/or death from the traumatic injury prior to admission.
Obesity was determined as a pre-existing comorbidity documented in the trauma registry data and calculated from height and weight measurements when available (BMI= kilogram/meters 2 ). The latter was defi ned as obesity by a BMI≥30 kg/m 2 and used to validate the diagnosis in the registry.
Outcomes of interest were hospital Length of Stay (LOS), admission to the ICU, length of ICU stay and in-hospital mortality. Length of stay was dichotomized by the overall median value observed (4 days for hospital LOS, 5 days for ICU LOS). All statistical analyses were performed using SAS ® , version 9.4 (SAS Institute, Cary, NC). Differences in outcome between obese and nonobese patients were compared using independent sample t-tests and Chi square tests for continuous and categorical variables, respectively. P values less than 0.05 were considered to be statistically signifi cant. Odds ratios adjusted for age, sex and race describing the association between obesity and the aforementioned outcomes were generated using multiple logistic regression. Additionally, patient comorbidities that exceeded 5% prevalence in this cohort were

Discussion
Obesity represents one of the largest growing public health concerns worldwide. By 2030, it is projected that up to 51%  of men and 52% of women in the United States will be obese [17]. While a great deal of research has focused on the disease burden of medical comorbidities associated with obesity, trauma remains the leading cause of death in individuals 46 years old or younger and is the third leading cause of death among all age groups [18]. Previous work has demonstrated that obese patients have higher odds of sustaining medicallytreated injuries [8,19]. Although the effect of obesity on traumatically injured patients has produced inconsistent results in the literature [5,[20][21][22][23], the present study contributes to a growing body of work reporting that obese trauma patients have signifi cantly higher mortality, increased complications and worse outcomes compared to their nonobese counterparts [3,6,12,13,24].
Consistent with previous studies, obese patients who sustained fractures were found to be signifi cantly more likely to have increased hospital lengths of stay [6,7,23,[25][26][27][28], more frequent admissions to the ICU and longer associated lengths of stay in the ICU [6,13,28,29]. Furthermore, after adjusting for The authors noted that the study was underpowered to detect a statistical difference between these two groups in terms of pulmonary complications, multiple organ failure and mortality [6]. In a study utilizing data from the NTDB, Belmont, et al. found that while obesity was a signifi cant risk factor for pulmonary and cardiac complications following hip fractures, it was not a risk factor for mortality [35]. Another study by  [13,23]. In another study investigating the impact of obesity on pediatric patients who sustained lower extremity fractures, obese patients were found to have sustained more severe injuries and thus were more likely to be admitted to the ICU (Relative Risk (RR) = 1.68; 95% CI, 1.10-2.55) and die during the hospitalization (RR= 3.45; 95% CI, 1.14-10.41). However, when adjusting for Injury Severity Score (ISS), these associations were no longer signifi cant [29]. In light of these varied fi ndings, further investigation is warranted to characterize the effect of obesity on mortality in patients sustaining orthopaedic fractures.
Recent literature suggests that obesity is protective against hip fractures and is associated with decreased mortality, the so called "obesity paradox" [36][37][38][39][40]. However, an analysis conducted across fracture sites in this study demonstrated that isolated femoral neck fractures were signifi cantly associated with mortality in this cohort of orthopaedic trauma patients.
Additionally, isolated humerus fractures were also found to increase the risk of mortality in obese individuals. Obese postmenopausal women have previously been shown to be at a signifi cantly increased risk of sustaining proximal humerus fractures compared to their nonobese counterparts (RR= 1.28, P= 0.018) [39]. In a study by Bercik et al., humerus fractures were found to be associated with a relatively high mortality rate (11.96%) which the authors attributed to the association with a high energy mechanism and close proximity to the vital structures of the head and thorax [41].  increasing BMI is associated with greater complications and worse perioperative outcomes [6,30], this study design based on a diagnosed comorbidity did not allow for such an analysis to be conducted. Additionally, the nonobese cohort in this study did not exclude underweight trauma patients (BMI<18.5), who have also been shown to have inferior outcomes as well [4,48,49]. Thus, this may have minimized the differences observed in outcomes between obese and nonobese patients.
Finally, utilizing our institution's trauma registry allowed us to evaluate the outcomes of a very large patient population, but also limited the number of outcomes that could be investigated.

Conclusion
The growing epidemic of obesity has profound implications for the care of orthopaedic trauma patients. This study provides further evidence demonstrating inferior outcomes associated with this challenging population and highlights the need for continued research on optimization of care of obese patients. Orthopaedic surgeons must be aware of the potential complications associated with obesity and have strategies in place to avoid and judiciously manage these complications should they arise. Furthermore, as our healthcare system transitions to a bundled payment format, it is imperative for orthopaedic surgeons to understand the impact that nonmodifi able risk factors portend in optimizing patient care in the acute fracture care setting. By better understanding the risks related to obesity and its associated comorbidities, treatment strategies can be tailored to patients with the goal of improving outcomes and minimizing healthcare cost.